It is known to produce hard and soft contact lenses in an automated production process with reusable moulds. To ensure the quality of the contact lenses obtained in the automated production process, the finished contact lenses must be optically inspected. However, in particular soft contact lenses are difficult to handle using mechanical means, and it is known to hold these in a water-filled cuvette for the purpose of optical testing.
U.S. Pat. No. 4,260,252 discloses a method and apparatus for immobilizing a contact lens without distortion to facilitate accurate measurement of its physical dimension. The wire-type support member is disposed to interact with the lens through surface tension effects of the liquid to immobilize the lens on the surface of the liquid whereon the lens is floated just out of contact with the support member.
It has been found previously that a contact lens, when inserted into and immersed in a water bath, always orients itself with the concave side facing upwards. Further, it is known, that contact lenses typically have a density at least slightly higher than water, therefore once completely immersed they are slowly sinking to the bottom of a water-filled cuvette. These properties are made use of in the following optical testing methods known in the art.
EP 1105708 A1 discloses a cuvette for optical inspection of ophthalmic lenses with a lens support having an indentation (for positioning the lens on the lens support) and the lens support having an optically finished surface (for avoiding optical distortion). Inspection is carried out while the lens is resting on the optically finished surface of the lens support.
WO 03/016855 A1 discloses a cuvette for lens inspection, said cuvette comprising a hollow space which is filled with a liquid and has an axis coinciding, in the test position of the cuvette, with the optical axis of the inspection system, and, in the test position of the cuvette, the hollow space is delimited from above by a viewing glass for the optical test and has, underneath the viewing glass, a seat, in particular a test trough, for the ophthalmic lens, wherein between viewing glass and test trough at least one insertion channel opens into the hollow space, the ophthalmic lens being able to be inserted into the hollow space through the outer insertion opening of said insertion channel. Inspection is carried out, while the lens is resting on the test trough.
As the upper surface of the test trough has direct contact with the lens, the imperfections of the surface are in the same focal plane of the inspection system as the lens and it may be difficult to distinguish between defects in the contact lens and defects or dirt on or in the test trough.
It is known for these type of inspection systems that it is necessary to ensure that the liquid and the viewing glasses (in particular if they act as the lens support) as they are situated in the optical path are clean and free of imperfections. Further, there must be no air bubbles present between liquid and viewing glasses, in particular in the field of focus of the inspection system. In an industrial production environment it is very often not possible to fully meet these demands.
A remaining problem not solved by the above mentioned inspection systems therefore is the optical quality of the test trough surface facing towards the hollow space, i.e. the lens support. In particular said lens support may have dirt, air bubbles or scratches on said surface, i.e. in the field of focus, which may adversely affect the optical inspection of the lens.
The object of the invention is to eliminate such adverse effects on the optical inspection of the lens as far as possible.
According to the invention, the object is achieved by the fact that the lens support is removed for inspection of the lens, thereby leaving the lens freely floating during optical inspection. Any detrimental effect of dirt, air bubbles or scratches on a surface other than the lens surface, which could adversely affect the optical inspection, are thereby eliminated.